Stop listening to POWER_SAVE_MODE_CHANGING broadcast.

The POWER_SAVE_MODE_CHANGING broadcast is sent at the same time as the
POWER_SAVE_MODE_CHANGED broadcast. Since broadcasts are asynchronous,
there's no reason to have both or listen to both, especially since it
potentially lead to inconsistency.

Bug: 79580230
Test: Android builds
Change-Id: I5c0448e98cc83a0d0d02e95f477e6632f79fd039